Methods for preparing isothiosemicarbazones have been disclosed in Bokin Bobai, Vol. 9, No. 12, pp. 551-561 (1981). Furthermore, Bokin Bobai discloses that certain of the compounds useful as antiviral compounds in the present invention have weak antibacterial activity. In addition, certain thiosemicarbazones or amidinohydrazone compounds have heretofore been known to have an antiviral activity, as described in Kitasato Arch. of Exp. Med., Vol. 46, pp. 73-81 (1973); ibid., Vol. 48, pp. 23-30 (1975); ibid., Vol. 48, pp. 125-130 (1975); ibid., Vol. 48, pp. 165-170 (1975); ibid., Vol. 48, pp. 171-181 (1975); ibid., Vol. 50, pp. 39-46 (1977); and Nature, Vol. 181, pp. 352-353 (1958).